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| United States Patent |
5,647,918
|
|
Kawana
, et al.
|
July 15, 1997
|
Bainite wire rod and wire for drawing and methods of producing the same
Abstract
This invention provides bainite wire rod and wire excellent in drawability
and methods of producing the same.
The bainite wire rod or wire is characterized in that it contains, in
weight percent, C: 0.70-1.20%, Mn: 0.30-0.90% and Si: 0.15-1.00%, further
contains as alloying components one or both of Al: 0.006-0.100% and Ti:
0.01-0.35%, if required contains Cr: 0.10-0.50%, and is limited to P: not
more than 0.02% and S: not more than 0.01%, the remainder being Fe and
unavoidable impurities, and has tensile strength and reduction of area
determined by the following equations (1) and (2),
TS.ltoreq.85.times.(C)+60 (1)
RA.gtoreq.-0.875.times.(TS)+158 (2)
where
C: carbon content (wt %),
TS: tensile strength (kgf/mm.sup.2), and
RA: reduction of area (%).
| Inventors:
|
Kawana; Akifumi (Chiba, JP);
Oba; Hiroshi (Chiba, JP);
Ochiai; Ikuo (Chiba, JP);
Nishida; Seiki (Chiba, JP)
|
| Assignee:
|
Nippon Steel Corporation (Tokyo, JP)
|
| Appl. No.:
|
532755 |
| Filed:
|
October 5, 1995 |
| PCT Filed:
|
April 6, 1994
|
| PCT NO:
|
PCT/JP94/00575
|
| 371 Date:
|
October 5, 1995
|
| 102(e) Date:
|
October 5, 1995
|
| PCT PUB.NO.:
|
WO94/23086 |
| PCT PUB. Date:
|
October 13, 1994 |
Foreign Application Priority Data
| Current U.S. Class: |
148/320; 148/333; 148/598; 148/599 |
| Intern'l Class: |
C21D 008/06; C22C 038/14 |
| Field of Search: |
148/598,599,320,333
|
References Cited
U.S. Patent Documents
| 4840686 | Jun., 1989 | Arnett et al. | 148/320.
|
| Foreign Patent Documents |
| 53-56122 | May., 1978 | JP | 148/333.
|
Primary Examiner: Yee; Deborah
Attorney, Agent or Firm: Wendroth, Lind & Ponack
Claims
We claim:
1. Bainite wire rod or wire for drawing which consists
essentially of, in weight percent,
C: 0.70-1.20%,
Mn: 0.30-0.90% and
Si: 0.15-1.00%,
further consisting of, as alloying components, one or both of
Al: 0.006-0.100% and
Ti: 0.01-0.35%,
is limited to
P: not more than 0.02% and
S: not more than 0.01%,
the remainder being Fe and unavoidable impurities, and which has a
microstructure of not less than 80% upper bainite texture in terms of area
ratio and an Hv of not more than 450, and has tensile strength and
reduction of area determined by the following equations (1) and (2),
TS.ltoreq.85.times.(C)+60 (1)
RA.gtoreq.-0.875.times.(TS)+158 (2)
where
C: carbon content (wt %),
TS: tensile strength (kgf/mm.sup.2), and
RA: reduction of area (%).
2. Bainite wire rod or wire for drawing according to claim 1 which has
tensile strength not exceeding 140 kgf/mm.sup.2.
3. Bainite wire rod or wire for drawing according to claim 1 which further
consists essentially of Cr: 0.10-0.50% as an alloying component.
4. A method of producing bainite wire rod for drawing which comprises
rolling into wire rod a steel slab of a composition which
contains, in weight percent,
C: 0.70-1.20%,
Mn: 0.30-0.90% and
Si: 0.15-1.00%,
further contains as alloying components one or both of
Al: 0.006-0.100% and
Ti: 0.01-0.35%,
is limited to
P: not more than 0.02% and
S: not more than 0.01%,
the remainder being Fe and unavoidable impurities,
cooling the rolled wire rod from a temperature range of
1100.degree.-755.degree. C. to the temperature range of
350.degree.-500.degree. C. at a cooling rate of 60.degree.-300.degree.
C./sec, and
holding it in this temperature range for not less than a period of Y sec
determined by the following equation (3),
Y=exp (19.83-0.0329.times.T) (3)
where
T: holding temperature (.degree.C.).
5. A method of producing bainite wire rod for drawing according to claim 4
wherein the starting steel slab further contains Cr: 0.10-0.50% as an
alloying component.
6. A method of producing bainite wire for drawing which comprises
heating to a temperature range of 1100.degree.-755.degree. C. wire of a
composition which
contains, in weight percent,
C: 0.70-1.20%,
Mn: 0.30-0.90% and
Si: 0.15-1.00%,
further contains as alloying components one or both of
Al: 0.006-0.100% and
Ti: 0.01-0.35%,
is limited to
P: not more than 0.02% and
S: not more than 0.01%,
the remainder being Fe and unavoidable impurities,
cooling the heated wire to a temperature range of 350.degree.-500.degree.
C. at a cooling rate of 60.degree.-300.degree. C./sec, and
holding it in this temperature range for not less than a period of Y sec
determined by the following equation (3),
Y=exp (19.83-0.0329.times.T) (3)
where
T: holding temperature (.degree.C.).
7. A method of producing bainite wire for drawing according to claim 6
wherein the starting wire further contains Cr: 0.10-0.50% as an alloying
component.
Description
TECHNICAL FIELD
This invention relates to bainite wire rod and wire for drawing and methods
of producing the same.
In this invention, "wire rod," when termed as a product, means wire rod
processed for drawing by subjecting it to direct heat treatment
immediately after rolling from a steel slab, while, "wire," when termed as
a product, means wire subjected to heat treatment in preparation for
drawing before drawing or after hot rolling and wire subjected to heat
treatment for secondary drawing after being subjected to primary drawing
by cold working following hot rolling.
BACKGROUND ART
Wire rod and wire are ordinarily drawn into a final products matched to the
purpose of use. Before conducting the drawing process, however, it is
necessary to put the wire rod or wire in a condition for drawing.
In the case of high-carbon steel wire rod or wire, the prior art requires
that a mixed texture of uniform, fine pearlite and a small amount of
pro-eutectoid ferrite be established before drawing, and, therefore, a
special wire rod or wire heat treatment called "patenting" is conducted.
This treatment heats the wire rod or wire to the austenite formation
temperature and then cools it at an appropriate cooling rate to complete
pearlite transformation, thereby establishing a mixed texture of fine
pearlite and a small amount of pro-eutectoid ferrite.
In the wire rod production method of Japanese Patent Publication No. Sho
60-56215, a heat treatment is conducted for obtaining a mixed texture of
fine pearlite and a small amount of pro-eutectoid ferrite by immersing the
wire rod heated to the austenite formation temperature in molten salt and
then cooling it from 800.degree.-600.degree. C. at a cooling rate of
15.degree.-100.degree. C./sec.
However, pearlite texture involves the problems of ductility degradation
during drawing at a high reduction of area and of cracking in twist test
(hereinafter referred to as "delamination").
The object of this invention is to provide wire rod or wire excellent in
ductility and not giving rise to the foregoing problems during drawing,
and to provided methods of producing the same.
DISCLOSURE OF THE INVENTION
For achieving this object, the present invention provides bainite-texture
wire rod or wire having a chemical composition containing C, Mn, Si, and
one or both of Al and Ti in an amount specified by the invention and, if
required, further containing a specified amount of Cr, the upper limit
value of P and S content being restricted, and further having prescribed
tensile strength and reduction of area.
For achieving this object, the present invention also provides bainite wire
rod or wire by increasing the cooling rate up to the nose position in the
TTT diagram during cooling of wire rod after hot rolling or during heat
treatment of wire after heat treatment at austenite formation temperature,
thereby preventing formation of pearlite texture, and then isothermally
holding the wire rod or wire at 350.degree.-500.degree. C. In other words,
following rolling of the wire rod or heating of the steel wire it is
cooled from the temperature range of 1100.degree.-755.degree. C. to the
temperature range of 350.degree.-500.degree. C. at a cooling rate of
60.degree.-300.degree. C./sec and maintained at this temperature for at
least a specified period to suppress formation of micromartensite texture
and thus provide bainite-texture wire rod or wire excellent in
drawability, whereby there is obtained wire rod or wire excellent in
drawability even at a high reduction of area.
Specifically, the gist of the invention is as set out below.
(1) Bainite wire rod or wire for drawing characterized in that
it contains, in weight percent,
C: 0.70-1.20%,
Mn: 0.30-0.90% and
Si: 0.15-1.00%,
further contains as alloying components one or both of
Al: 0.006-0.100% and
Ti: 0.01-0.35%,
is limited to
P: not more than 0.02% and
S: not more than 0.01%,
the remainder being Fe and unavoidable impurities, and
has tensile strength and reduction of area determined by the following
equations (1) and (2),
TS.ltoreq.85.times.(C)+60 (1)
RA.gtoreq.-0.875.times.(TS)+158 (2)
where
C: carbon content (wt %),
TS: tensile strength (kgf/mm.sup.2), and
RA: reduction of area (%).
(2) Bainite wire rod or wire for drawing according to paragraph 1 above
characterized in that it further contains Cr: 0.10-0.50% as an alloying
component.
(3) Bainite wire rod or wire for drawing according to paragraph 1 or 2
above characterized in that it has a microstructure of not less than 80%
upper bainite texture in terms of area ratio and an Hv of not more than
450.
(4) A method of producing bainite wire rod for drawing characterized by
rolling into wire rod a steel slab of a composition which
contains, in weight percent,
C: 0.70-1.20%,
Mn: 0.30-0.90% and
Si: 0.15-1.00%,
further contains as alloying components one or both of
A1: 0.006-0.100% and
Ti: 0.01-0.35%,
is limited to
P: not more than 0.02% and
S: not more than 0.01%,
the remainder being Fe and unavoidable impurities,
cooling the rolled wire rod from the temperature range of
1100.degree.-755.degree. C. to the temperature range of
350.degree.-500.degree. C. at a cooling rate of 60.degree.-300.degree.
C./sec, and
holding it in this temperature range for not less than a period of Y sec
determined by the following equation (3),
Y=exp(19.83-0.0329.times.T) (3)
where
T: holding temperature (.degree.C.).
(5) A method of producing bainite wire rod for drawing according to
paragraph 4 above wherein the starting steel slab further contains Cr:
0.10-0.50% as an alloying component.
(6) A method of producing bainite wire for drawing characterized by
heating to the temperature range of 1100.degree.-755.degree. C. wire of a
composition which
contains, in weight percent,
C: 0.70-1.20%,
Mn: 0.30-0.90% and
Si: 0.15-1.00%,
further contains as alloying components one or both of
Al: 0.006-0.100% and
Ti: 0.01-0.35%,
is limited to
P: not more than 0.02% and
S: not more than 0.01%,
the remainder being Fe and unavoidable impurities,
cooling the heated wire to the temperature range of 350.degree.-500.degree.
C. at a cooling rate of 60.degree.-300.degree. C./sec, and
holding it in this temperature range for not less than a period of Y sec
determined by the following equation (3),
Y=exp (19.83-0.0329.times.T) (3)
where
T: holding temperature (.degree.C.).
(7) A method of producing bainite wire for drawing according to paragraph 6
above wherein the starting wire further contains Cr: 0.10-0.50% as an
alloying component.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a diagram showing a heat treatment pattern of the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
The reasons for the restrictions on the constituent elements of the
invention will now be discussed.
The reasons for the restrictions on the chemical compositions of the
starting steel slab and wire will be described in the following.
C is a fundamental element governing strength and ductility, strength
increasing with higher carbon content. The lower limit of C content is set
at 0.70 wt % for ensuring hardenability and strength and the upper limit
is set at 1.20 wt % for preventing formation of pro-eutectoid cementite.
Si is added at not less than 0.15 wt % as a deoxidizing agent. Si is also
an element which solid-solution hardens the steel and is further capable
of reducing wire relaxation. However, since Si reduces the amount of scale
formation, degrading mechanical scaling property, and also lowers the
lubricity somewhat, the upper limit of Si content is therefore set at 1.00
wt %.
Mn is added at not less than 0.30 wt % as a deoxidizing agent. Although Mn
is an element which strengthens the steel by its presence in solid
solution, increasing the amount added increases the likelihood of
segregation at the center portion of the wire rod. Since the hardenability
of the segregated portion increases, shifting the finishing time of
transformation toward the long period side, the untransformed portion
becomes martensite, leading to wire breakage during drawing. The upper
limit of Mn content is therefore set at 0.90 wt %.
Although Al acts as a deoxidizer and is also the most economical element
for obtaining fine-grained austenite by fixing N in the steel, Al is not a
required element when the N content is low. The upper limit of N content
is set at 0.100 wt % in consideration of increase in nonmetallic
inclusions and the lower limit is set at 0.006 wt %, where the effect of
Al appears.
Ti is already currently used in Ti-deoxidized steels, mainly for adjusting
the austenite crystal grains of ordinary carbon steel. The upper limit of
Ti content is set at 0.35 wt % for suppressing increase of Ti inclusions
and suppressing formation of solid solution carbo-nitrides in the steel.
The lower limit is set at 0.01 wt %, where these actions appear to an
effective degree.
The wire rod and the wire of this invention contain one or more of the two
elements A1 and Ti.
Since P and S precipitate at the grain boundaries and degrade the steel
properties, it is necessary to hold their contents as low as possible. The
upper limit of P content is set at 0.02 wt % and the upper limit of S
content is set at 0.01 wt %.
Cr, an element which increases steel strength, is added as occasion
demands. While increasing the amount of Cr increases strength, it also
increases hardenability and moves the transformation finishing time line
toward the long period side. Since this prolongs the time required for
heat treatment, the upper limit of Cr content is set at 0.50 wt %, while
the lower limit thereof is set at 0.10 wt % for increasing strength.
The rolling conditions and heat treatment conditions for obtaining the
bainite wire rod and wire of this invention will now be discussed.
The reason for defining the temperature from which cooling is started
following wire rod rolling and the wire heating temperature as
755.degree.-1100.degree. C. is that 755.degree. C. is the lower limit
temperature of austenitic transformation while abnormal austenite grain
growth occurs when the temperature exceeds 1100.degree. C.
The reason for defining the cooling rate from the start of wire rod or wire
cooling to the isothermal holding temperature range of
350.degree.-500.degree. C. as 60.degree.-300.degree. C./sec is that
60.degree. C./sec is the lower limit of the critical cooling rate for
formation of the upper bainite texture while 300 .degree. C./sec is the
upper limit of the industrially feasible cooling rate.
The reason for setting the isothermal holding temperature following cooling
as 350.degree.-500.degree. C. is that 350.degree. C. is the lower limit
temperature for upper bainite texture formation while 500.degree. C. is
the upper limit temperature for upper bainite texture formation.
The required isothermal holding time in the temperature range between
350.degree.-500.degree. C. is calculated from the transformation finishing
time line in the TTT diagram. If the immersion time in the cooling tank is
insufficient, however, martensite forms and becomes a cause for wire
breakage during drawing. Since holding for not less than the finishing
time of transformation is therefore required, the holding time in the
temperature range of 350.degree.-500.degree. C. is defined as the time Y
sec determined by the following equation (3).
Y=exp (19.83-0.0329.times.T) (3)
where T: heat treatment temperature (.degree.C.).
The reasons for the limitations on the characteristics of the wire rod and
wire which are products of the invention will now be discussed.
Since tensile strength is strongly dependent on C content, it is given in
terms of its relationship with C content in the manner of equation (1). In
wire rod or wire having bainite texture, the cementite precipitation is
coarser than it is in prior art wire rod and wire having pearlite texture
and, therefore, the tensile strength is lower for the same composition. In
wire-drawing, lowering the initial tensile strength improves the
drawability and enables drawing to a high reduction of area. The tensile
strength is therefore limited in the manner of equation (1) as the limit
up to which the drawability is not degraded. When the upper limit is
exceeded, the drawability is degraded, causing the occurrence of breakage
or delamination in the course drawing.
The reduction of area is an important factor indicative of ease of
processing during drawing. Even at the same tensile strength, raising the
reduction of area lowers the work hardening rate and enables drawing to a
high reduction of area. In wire rod having bainite texture, the cementite
precipitation is coarser than it is in prior art wire rod having pearlite
texture and, therefore, the reduction of area is higher for the same
tensile strength. The reduction of area is therefore limited in the manner
of equation (2) as the limit up to which the drawing limit is not
degraded. When the lower limit is not reached, the drawability is
degraded, causing the occurrence of breakage or delamination in the course
drawing.
In addition to having the tensile strength and reduction of area prescribed
in the foregoing, the invention wire rod or wire having bainite texture
further has a microstructure of not less than 80% upper bainite texture in
terms of area ratio and an Hv of not more than 450. As a result, its
drawability is even further enhanced.
EXAMPLES
Example 1
Table 1 shows the chemical compositions of tested steel specimens.
A-D in Table 1 are invention steels and E and F are comparison steels.
Steel E has a C content exceeding the upper limit and steel F has a Mn
content exceeding the upper limit.
The specimens were produced by casting 300.times.500 mm slabs with a
continuous casting machine and then bloom pressing them into 122-mm square
slabs.
After these slabs had been rolled into billets, they were rolled into wire
rods of the diameters shown in Table 2 and subjected to DLP (Direct Lead
Parenting) cooling.
The wire rods were drawn to 1.00 mm.phi. at an average reduction of area of
17% and subjected to tensile test and twist test.
The tensile test was conducted using the No. 2 test piece of JISZ2201 and
the method described in JISZ2241.
In the twist test, the specimen was cut to a test piece length of 100d+100
and rotated at a rotational speed of 10 rpm between chucks spaced at 100d.
d represents the wire diameter.
The characteristic values obtained in this manner are also shown in Table
2.
No. 5-No. 10 are comparative steels.
In No. 5, pearlite which formed because the cooling rate was too slow
reduced the drawability, leading to breakage during drawing.
In No. 6, pearlite which formed because the isothermal transformation
temperature was too high reduced the drawability, leading to breakage
during drawing.
In No. 7, martensite which formed because the isothermal transformation
treatment time was short reduced the drawability, leading to breakage
during drawing.
In No. 8, bainite texture did not form because the temperature from which
cooling was started was too low, reducing the drawability and leading to
breakage during drawing.
In No. 9, pearlite which formed because the C content was too high reduced
the drawability.
In No. 10, micromartensite which formed in conjunction with central
segregation caused by an excessively high Mn content reduced the
drawability.
TABLE 1
__________________________________________________________________________
Chemical Compositions of Tested Steel Specimens
Chemical Compositions (wt %)
Symbol
C Si Mn P S Cr Al Ti N O Remark
__________________________________________________________________________
A 0.960
0.18
0.40
0.012
0.009
0.25
-- 0.30
0.0054
0.0029
Invention
B 0.930
0.15
0.30
0.010
0.008
0.28
0.080
0.01
0.0031
0.0030
Invention
C 1.120
0.16
0.39
0.013
0.007
0.35
0.070
-- 0.0034
0.0025
Invention
D 0.900
0.20
0.35
0.015
0.008
-- -- 0.02
0.0055
0.0036
Invention
E 1.290
0.11
0.40
0.018
0.008
0.20
0.010
0.01
0.0034
0.0037
Comparison
F 0.980
0.30
1.80
0.016
0.009
0.22
0.010
0.01
0.0037
0.0029
Comparison
__________________________________________________________________________
TABLE 2
__________________________________________________________________________
Wire Rod Rolling Conditions and Characteristic Values of Tested Steel
Specimens
Cooling
Rolled wire rod
After drawing (diameter: 1.00 mm)
tank TS Reduc-
Bainite TS Reduc-
Twist
Diameter
T.sub.0
V.sub.1
T.sub.1
t.sub.1
kgf/
tion
texture kgf/
tion
value
Delami-
No.
Symbol
mm .phi.
.degree.C.
.degree.C./s
.degree.C.
s mm.sup.2
% ratio %
Hv mm.sup.2
% (times)
nation
Remark
__________________________________________________________________________
1 A 4.0 950
120
450
160
140
50 95 430
260 40 25 No Invention
2 B 4.5 1000
150
470
100
130
53 90 420
275 42 30 No Invention
3 C 5.0 1050
200
480
70
140
58 90 420
280 43 28 No Invention
4 D 5.5 800
160
490
50
120
55 85 450
268 41 26 No Invention
5 A 5.0 1000
50
450
160
150
25 30 550
Broke at 1.3 mm .phi.
Comparison
6 B 5.0 1050
130
550
80
150
25 30 550
Broke at 1.2 mm .phi.
Comparison
7 C 5.5 1100
120
490
20
170
15 60 550
Broke at 1.4 mm .phi.
Comparison
8 D 5.5 740
120
480
60
140
45 0 460
Broke at 1.3 mm .phi.
Comparison
9 E 5.5 1050
130
480
80
160
35 70 550
290 20 13 Yes Comparison
10 F 5.5 1050
120
470
50
170
13 60 600
270 35 19 Yes Comparison
__________________________________________________________________________
T.sub.0 : Cooling start temperature
V.sub.1 : Cooling rate
T.sub.1 : Cooling temperature
t.sub.1 : Cooling time
Example 2
Table 3 shows the chemical compositions of tested steel specimens.
A-D in Table 3 are invention steels and E and F are comparison steels.
Steel E has a C content exceeding the upper limit and steel F has a Mn
content exceeding the upper limit.
The wires were transformed to austenitic texture under the conditions shown
in Table 4. After heat treatment they were drawn to 1.00 mm.phi. at an
average reduction of area of 17% and subjected to tensile test and twist
test.
The tensile test was conducted using the No. 2 test piece of JISZ2201 and
the method described in JISZ2241.
In the twist test, the specimen was cut to a test piece length of 100d +100
and rotated at a rotational speed of 10 rpm between chucks spaced at 100d.
d represents the wire diameter.
The characteristic values obtained in this manner are also shown in Table
4.
No. 1-No. 4 are invention steels. Since they satisfy all heat treatment
conditions of the invention, they can be drawn into wire that does not
exhibit delamination even at 1.00 mm .phi. following drawing.
No. 5-No. 10 are comparative steels.
In No. 5, pearlite which formed because the cooling rate was too slow
reduced the drawability, leading to breakage during drawing.
In No. 6, pearlite which formed because the isothermal transformation
temperature was too high reduced the drawability, leading to breakage
during drawing.
In No. 7, martensite which formed because the isothermal transformation
treatment time was short reduced the drawability, leading to breakage
during drawing.
In No. 8, the bainite texture ratio was zero because the heating
temperature was too low, reducing the drawability and leading to breakage
during drawing.
In No. 9, pearlite which formed because the C content was too high reduced
the drawability.
In No. 10, pearlite formed and the reduction of area was low because the Mn
content was too high, reducing the drawability.
TABLE 3
__________________________________________________________________________
Chemical Compositions of Tested Steel Specimens
Chemical Compositions (wt %)
Symbol
C Si Mn P S Cr Al Ti N O Remark
__________________________________________________________________________
A 0.960
0.18
0.40
0.012
0.009
0.25
-- 0.30
0.0054
0.0029
Invention
B 0.930
0.15
0.30
0.010
0.008
0.28
0.080
0.01
0.0031
0.0030
Invention
C 1.120
0.16
0.39
0.013
0.007
0.35
0.070
-- 0.0034
0.0025
Invention
D 0.900
0.20
0.35
0.015
0.008
-- -- 0.02
0.0055
0.0036
Invention
E 1.290
0.11
0.40
0.018
0.008
0.20
0.010
0.01
0.0034
0.0037
Comparison
F 0.980
0.30
1.80
0.016
0.009
0.22
0.010
0.01
0.0037
0.0029
Comparison
__________________________________________________________________________
TABLE 4
__________________________________________________________________________
Wire Heat Treatment Conditions and Characteristic Values of Tested Steel
Specimens
After heat treatment,
Cooling
before drawing After drawing (diameter: 1.00 mm)
tank TS Reduc-
Bainite TS Reduc-
Twist
Diameter
T.sub.0
V.sub.1
T.sub.1
t.sub.1
kgf/
tion
texture kgf/
tion
value
Delami-
No.
Symbol
mm .phi.
.degree.C.
.degree.C./s
.degree.C.
s mm.sup.2
% ratio %
Hv mm.sup.2
% (times)
nation
Remark
__________________________________________________________________________
1 A 3.0 950
120
450
160
140
50 95 430
260 40 25 No Invention
2 B 4.0 1000
150
470
100
130
53 90 420
275 42 30 No Invention
3 C 4.5 1050
200
480
70
140
58 90 420
280 43 28 No Invention
4 D 5.5 800
160
490
50
120
55 85 450
268 41 26 No Invention
5 A 5.0 1000
50
450
160
150
25 30 550
Broke at 1.3 mm .phi.
Comparison
6 B 5.0 1050
130
550
80
145
46 50 480
Broke at 1.2 mm .phi.
Comparison
7 C 4.8 1100
120
490
20
170
15 60 550
Broke at 1.4 mm .phi.
Comparison
8 D 5.0 740
120
480
60
140
45 0 460
Broke at 1.3 mm .phi.
Comparison
9 E 4.0 1050
130
480
80
160
35 70 550
290 20 13 Yes Comparison
10 F 3.5 1050
120
470
50
170
13 60 600
270 35 19 Yes Comparison
__________________________________________________________________________
T.sub.0 : Heating temperature
V.sub.1 : Cooling rate
T.sub.1 : Cooling temperature
t.sub.1 : Cooling time
Industrial Applicability
As discussed in the foregoing, since the wire rod or wire produced in
accordance with this invention can be drawn to an appreciably higher
reduction of area than possible by the prior art method, it has improved
delamination resistance property. The invention is therefore able to
provide bainite wire rod and wire that are excellent in drawability.
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